"Individuals who have gastric bypass surgery lose a significant amount of weight. At two years, they had lost 35 percent of their initial body weight. At six years, it was about 28 percent, which shows a pretty durable weight loss," said study lead author Ted Adams, an adjunct associate professor in the division of cardiovascular genetics at the University of Utah School of Medicine in Salt Lake City.

"At six years, in those patients who had type 2 diabetes prior to surgery, 62 percent no longer had a diagnosis of diabetes. There was also significant remission in high blood pressure, high cholesterol and high triglycerides," said Adams.

The results are published in the Sept. 19 issue of the Journal of the American Medical Association.

Dr. Anita Courcoulas, chief of minimally invasive bariatric and general surgery at the University of Pittsburgh Medical Center and author of an accompanying editorial, also pointed out that many cases of type 2 diabetes were prevented in the weight loss surgery group. "Only 2 percent of people in the gastric bypass group developed type 2 diabetes," she said, whereas in the study's control groups, the rate of type 2 diabetes development was as high as 17 percent.

Adams' study included more than 1,150 severely obese people who underwent gastric bypass surgery between 2000 and 2011. The average body mass index, a measure of body fat, was 46. Anything over 40 is considered morbidly obese.

Courcoulas said weight loss surgery generally is considered only if someone has a BMI of at least 40, or a BMI between 35 and 40 along with a serious medical condition, such as type 2 diabetes or high blood pressure.

The study also included two control groups. One control group had 417 people who had considered surgery, but didn't have it. The other control group had 321 randomly selected severely obese people who hadn't considered weight loss surgery.

In gastric bypass surgery, doctors divide the stomach into two sections and connect the small top section, or pouch, to the small intestine. Because the pouch can only hold a small amount of food, the body absorbs fewer calories.

In the United States, where one-third of adults are obese and at risk of serious weight-related health problems, weight loss surgery is becoming increasingly common.

"The study showed that gastric bypass led to durable weight loss and a durable impact on health conditions," said Courcoulas.

Surgery may not be for everyone, however. "Patients should talk to their physicians and focus on the risks of their current health problems, as well as future health risks and weigh those with the risks of surgery," said Adams. Lifestyle adjustments, such as diet modification and physical activity, should be a foundation for any change people want to make.

Two other studies, also in the current issue of JAMA, looked at different aspects of weight loss surgery, including gastric bypass and banding procedures. One study, conducted in Sweden, compared long-term health costs of slightly more than 2,000 obese people who underwent bariatric surgery and a similar number of age-matched obese people who did not have surgery (the control group).

After 20 years, the surgical group had an average weight loss of 18 percent of body weight compared to just 1 percent in the control group. In terms of actual weight, it was a difference of about 44 pounds. The researchers found that in the six years following surgery, the surgical patients used more inpatient and outpatient care. But, during years seven through 20, those who underwent surgery had fewer drug and cardiovascular disease costs.

"The Swedish study found that health care needs equalize over time, but what is really needed is a formal cost-effectiveness analysis," said Courcoulas.

The other study, conducted in Australia, compared 30 weight loss surgery patients to 30 people on a very low-calorie diet to see which group had a more significant improvement in sleep apnea symptoms. The surgery patients underwent a gastric banding procedure and lost an average of 61 pounds, while those on the diet lost about 11 pounds. Both groups experienced fewer sleep apnea episodes, but the difference between the two groups wasn't significant.

Courcoulas said this finding was "a little puzzling. It's hard to explain why there wasn't a relationship between weight loss and sleep apnea," given that the sleep disorder is associated with overweight and obesity. She added that "more work needs to be done here to understand the mechanism."